BEIRUT (AP) - The collapse of Lebanon's government plunged the country into deep political uncertainty Thursday after a year of relative stability, as the president began the process of putting a new administration together.

President Michel Suleiman asked Saad Hariri to stay on as caretaker prime minister after the Iranian-backed militant group Hezbollah and its allies resigned Wednesday and brought down Hariri's government. The crisis was the climax of tensions that have been simmering for months over the U.N. tribunal investigating the 2005 assassination of Hariri's father, former Prime Minister Rafik Hariri.

The tribunal is widely expected to indict members of Hezbollah soon, which many fear could rekindle violence in the tiny nation plagued for decades by war and civil strife.

Lebanon suffered through a devastating civil war from 1975-1990, a 1982 Israeli invasion to drive out Palestinian fighters in the south followed by a 20-year occupation of the south, a 2006 war between Israel and Hezbollah, and deadly sectarian fighting between the country's Sunnis and Shiites in 2008.

The collapse of the government ushers in the worst political crisis since 2008 in one of the most volatile corners of the Middle East.

Arab League chief Amr Moussa expressed concern that Lebanon could again descend into chaos.

"It is bad. It is tense. It is threatening," he said of the situation. "All of us have to work together in order to reach some kind of compromise," he told reporters in Doha, Qatar.

Israel also said it was worried about renewed violence on its northern border with Lebanon. Israeli troops in the north of the country were on alert Thursday.

Lebanon's 14-month-old unity government was an uneasy coalition linking bitter rivals - a Western-backed bloc led by Hariri and the Shiite Hezbollah - that was an attempt to stabilize the country. But in reality, it had been paralyzed for months because of disputes over the Hariri tribunal.

The president's office said in a statement he was accepting the resignations of 11 ministers - which amounted to the more than one-third of the 30-member Cabinet required to bring the government down.

But the president asked Hariri to continue managing the country's day-to-day affairs until a new cabinet is formed.

Hezbollah is supported by Syria and Iran and maintains an arsenal that far outweighs that of the national army.

At the heart of the dispute that brought down the government, Hezbollah denounces the Netherlands-based tribunal as a conspiracy by the U.S. and Israel and urging Hariri to reject any of its findings. But Hariri has refused to break cooperation with the tribunal.

Now, the chasm between the two sides is deepening with Hezbollah accusing Hariri's bloc of bowing to the West. Hezbollah's ministers timed their resignations to coincide with Hariri's meeting with President Barack Obama in Washington, forcing him to meet the American president as a caretaker prime minister.

Hariri was to hold talks in Paris on Thursday with French President Nicolas Sarkozy.

Suleiman was expected to begin consultations over the choice of a new prime minister Thursday. He was scheduled to meet with Parliament Speaker Nabih Berri, after which he was to set a date to begin polling lawmakers on their choice.

There were expectations of prolonged wrangling over the choice of prime ministerEINA KARAM